There should be no more then +/- 10% difference between the lowest and highest readings.
In your case, if I math this up correctly.
% difference = 100 - (172 / 145 * 100) = 15.69%
This is greater then the standard norm of +/- 10% so you do have a problem some where. I would couple this test with the fact you used 1.5+ quarts of oil in 50 hours.
You can do a wet test to isolate the issue to rings or valves.
So the 64k question is how long can I run the motor like this?
I don't know. It could continue to run ok for a long time or it could get worse in a couple of weeks.
Maybe enginenut will be around to give more guidance.